Electric valve protective system



Jam. 28,1936 F. MERTENS I 213299279 ELECTRIC VALVE PROTECTIVE SYSTEMFiled March 14, 1935 Patented Jan. 28, 1936 .UNl'l'ED STATES PA'IENTQFFIQE.

Franz Martens, Mannheim,

Germany, assigncr to Aktiengesellschaft Brawn Boveri dz Cie., Baden,Switzerland, a joint-stock company of Switzerland Application March 14,1935, Serial No. 10,984 in Germany November 11, 1933 11 Claims.

This invention relates in general to protective systems, and moreparticularly to means for preventing the continued flow of currentthrough an electric valve following an abnormal decrease of theimpedance thereof.

It is well known that electric valves of the high vacuum type present animpedance to the flow of current between the electrodes thereof whichimpedance may be controlled between predetermined limits by the use ofconductivity controlling means such as grids. It occasionally happensthat the conductivity of the valve suddenly increases to an extent suchthat the valve substantially constitutes a short circuit for the sourceof current connected therewith. The causes of such phenomenon are notWell understood, but it may be surmised that excessive local heating ata point of the cathode causes metal therefrom to be evaporated at a ratesuch that a path cam pable of conducting an arcing discharge isestablished thereby. If the resulting flow of current is prevented fromreaching too high a value, and if such flow of current is rapidlyinterrupted, the valve is generally not materially damaged and may beimmediately put back in operation so that the continuity of operation ofthe valve is only inappreciably disturbed. Such result is mostadvantageously obtained by shunting the valve by a gap so connected asto break down upon collapse of the impedance of the valve. If the valveis supplied with current from an electric current rectifier, the flow ofcurrent through the gap may then be interrupted by momentarilyenergizing the control electrodes of the rectifier at a negativepotential and the system may be returned to the normal operatingcondition thereof upon return of the gap to the insulating condition. Asthe breakdown of the gap occurs with a certain time lag, it is desirableto reduce the rate of increase of the flow of current through the valve,so that the current is prevented from reaching too high a valve beforethe breakdown of the gap. Such result is obtained by connecting areactor in series with the valve.

It is, therefore, among the objects of the present invention to providea protective system for an electric circuit by which the flow of currentis diverted from such circuit upon occurrence of abnormal operating condions therein.

Another object of the present invention is to provide an electric valveprotective system by which the rate of increase of the flow of currentthrough the valve upon collapse of the impedance thereof is reduced tothe greatest possible ex- 5; tent.

Another object of the present invention is to provide an electric valveprotective system by which the flow of current through the valve isdiverted therefrom upon breakdown of the impedance of the valve.

Another object of the present invention is to provide an electric valveprotective system by which the flow of current diverted from the valvemay be interrupted to thereby restore the normal operating condition ofthe system.

Objects and advantages other than those above set forth will be apparentfrom the following description when read in connection with the singlefigure of the accompanying drawing which diagrammatically illustratesthree embodiments of the present invention severally applied to theprotection of electric valves employed in a radio transmitting system.

Referring more particularly to the drawing by characters of reference,reference numerals 6, 1

and 8 designate electric valves of the three electrode high vacuum typeutilized in a radio transmitting system. Such valves may be connected inany circuit known in the art, typical connections being showntherebetween only for the purpose of making the drawing complete andthereby facilitating the understanding of the invention. Valves 8, l and8 are supplied with direct current from a rectifying system energizedfrom an alternating current supply line 9, and comprising a transformerl l and a valve 12 of any suitable type. Valve i2 is represented asbeing of the vapor type having a cathode 13 which is maintained incurrent conductive condition by any suitable means, such means beingwell known 5 bringing the control electrodes to a negative potentialwith respect to the potential of cathode In the present system, valve 52is accordingly operative when the control electrodes are connected,through the contacts of a relay I! with the positive terminal of thebattery It! having the negative terminal thereof connected with cathodei3. The flow of current through valve i2 ceases when the connections ofbattery 18 are reversed as a result of operation of relay IT.

The output terminals of the rectifying system are located at cathode l3and at the neutral point of the secondary winding of transformer l l.One of such terminals is connected with a plurality of reactors I9, 20and 25, of which some may be serially connected such as reactors I9 and26. Each valve 6, i and 8 is connected between the terminal of onereactor furthest from the source and the terminal of the rectifyingsystem with which the reactors are not connected. A plurality ofcapacitors 22, 23 and 2d are severally connected in parallel with valves6, l and 8. Valve 6 functions as an amplifying valve, the controlelectrode thereof being connected with the associated cathode through abias battery 26 and through the output circuit of an oscillating system2'! of any suitable type operable to produce electrical oscillations ofa frequency within the range of frequencies utilized for the productionof electromagnetic waves. The connection between oscillator 27 and thecontrol electrode of valve 6 may be controlled by a signaling key, orthe oscillations may be modulated by means of a microphone 28 for thepurpose of transmitting speech or other sounds.

Valves 7 ands are connected in the so-called push-pull connection, thecontrol electrode of each valve being connected with the associatedcathode through a common bias battery 29 shunted by a capacitor 3 l andthrough one of the portions of the secondary winding 33 of a transformerhaving a primary winding 32 connected in series with valve 6. Suchtransformer transmits to the control electrode circuits, modulatedoscillations from oscillator 21 amplified by the action of valve 6. Thevoltages across valves 7 and 8 are impressed on the primary winding 35of a transformer having a secondary winding 36 connected between anantenna 37 and ground at 38. Winding 35 is preferably shunted by acapacitor 39 tuned therewith for the frequency of oscillator 27, and theconnections between valves 7 and 8 and winding 34 preferably includeblocking capacitors ii: preventingthe undesired flow of direct currentfrom rectifier l2 through winding 34.

The circuits provided for protecting valves 6, I and 8 against excessiveflows of current resulting from breakdown of the impedance of the valvesare arranged somewhat difierently for each valve, for the purpose ofillustrating a few of the diiferent ways in which their connections canbe efiected. Each valve is associated with a pair of electrodes 4!defining a gap connected in parallel with the associated valve. Valve 6is connected in series with the primary winding 42 of a transformerhaving a secondary winding 53 connected in series with the associatedgap 2 l A resistor 64 may be inserted in series with the valve and withwinding 42, and another resistor 46 may be connected in series with gap4! and winding 53.

The winding d3 associated with valve 7 is not connected in series withassociated gap 49, but is connected with a second pair of electrodes t7defining a gap partly coextensive with gap 4!. The winding 43 associatedwith valve 8 is connected in series with a capacitor 38 across a gapdefined by one of electrodes ll and another elec' trode 49, such gapbeing partly coextensive with gap 6!. The coil of relay 8'! is connectedbetween cathode l3 and the terminals of reactors H9, 29 and El farthestfrom the cathode through gaps defined by electrodes 55, 52 and 53serially connected with resistors 5d, 56 and 5'5.

During normal operation of the system, relay I7 being in the positionshown and line 9 being energized, transformer H and valve l2 operate asa rectifying system equivalent to a source of direct current supplyingcurrent to valves 6, l and 8. The current flowing through such a systemgenerally contains alternating components in addition to the desiredunidirectional component, and the fiow of such alternating componentsthrough valve 6 is substantially prevented by the cooperating action ofreactor 1 9 and capacitor 22. The flow of current is likewise maintainedsubstantially uniform through valve 7 by the cooperating action ofreactors l9 and 29 and of capacitor 23, and also through valve 8 by thecooperating action of reactor 2! and capacitor 25.

The oscillations produced by oscillator 27 and modulated by microphone28 are impressed between the cathode and the control electrode of valve6 to cause the conductivity of valve 6 to vary within a predeterminedoperating range. The inductance of reactor l9 preventing the fiow ofcurrent therethrough from varying in response to the variations ofconductivity of valve 6, such variations of conductivity resulting insuccessive charges of capacitor 22 and discharges thereof throughreactor is through valve 6, to thereby cause the appearance in winding32 of alternating voltages similar to the voltages impressed between thecontrol electrodes and cathode of valve 6, but at greater amplitude.During such operation, the flow of current from rectifier 52 throughreactor l9 and valve 6 remains substantially constant, and alternatingcurrents may circulate between valve 6 and capacitor 22 irrespective ofthe rectifying action of valve 6 for the reason that the total currentflowing through valve 6 remains unidirectional.

The voltages induced in winding 33 and impressed between the controlelectrodes and cathodes of valves l and 8 cause the conductivities ofvalves l and 8 to vary to an extentv greater than the conductivity ofvalve 6. Reactors H, 213 and 2| prevent variation in the ilow of currentfrom rectifier 12 to valves 1 and 8 in response to such variations ofconductivity, and such conductivity changes therefore result in chargesand discharges of capacitors 23 and 25 through valves 1 and 8 similar tothe charges and discharges of capacitor 22 through valve 5, but atgreater amplitude. As a result the terminal voltages of valves 1 and 8and capacitors 23 and 2d oscillate at the frequency of oscillator 2?,the amplitude of such oscillations being in accordance with themodulation introduced by microphone 28, and the thus modulated voltagesare impressed on winding 34 through capacitors 6D to cause antenna 37 toradiate electromagnetic waves.

Upon occurrence of a sudden accidental breakdown of the impedance ofvalve 6, capacitor 22 immediately discharges through the valve. As aresult of such discharge, the flow of current through valve 6 suddenlyincreases at a rate considerably greater than any rate of increaseresulting from increases in conductivity caused by the control electrodeduring normal operation of the valve. Such rate of the increase of theflow of current causes the appearance in winding @2 of a voltageproportional thereto and inducing a corresponding voltage in winding Thevoltage of winding 53, superimposed on the voltage of winding 42 and thevoltage in valve 5, is impressed on gap 4! to cause the gap to breakdown.

Gap M is so arranged as to offer less impedance to the flow of currentthan valve 6 even when such valve is in the broken down condition, sothat the flow of current through valve 6 ceases and is transferred togap 4|. To obtain such re sult it may be necessary to insert a resistor44 in series with valve 6 to increase the voltage drop in the circuitthereof and cause transfer of the flow of current to gap 4|. Resistor 44should, of course, be of such low value as not to adversely affeet thenormal operation of valve 6. Windings 42 and 43 are so arranged that gap4| breaks down before the discharge current of capacitor 22 throughvalve 6 reaches more than a few times the value of the normal current ofvalve 6, so that the flow of current may be transferred to gap 4| beforereaching the maximum value thereof. As the breakdown of gap 4| is notinstantaneous but generally occurs with a certain time lag, it may bedesirable to somewhat reduce the rate of increase of the flow of currentthrough valve 5 by increasing the inductances of windings 42 and 32,such inductances being however always of magnitude too low to have anydetrimental effect on the normal operation of the system. A resistor 48may also be connected in series with gap 4| to cause damping of thedischarge of capacitor 22 through the gap.

As a result of the breakdown of valve 6 and of gap 4!, an actual shortcircuit is provided for the flow of current from rectifier i2 and alsofor the discharge of capacitors 23 and 24. During the initial flow ofexcessive current through valve 6 and the transfer of the flow ofcurrent to gap 4!, reactor l9 prevents a material increase in the flowof current supplied to valve 6 from valve l2, reactor 20 prevents anymaterial discharge of capacitor 23 through valve 6, and reactors 2i and9 prevent any material discharge of capacitor 24 through valve 6. Valve6 accordingly carries only substantially the discharge current ofcapacitor 22 during such period, thereby reducing to the greatestpossible extent the danger of damage to the valve resulting from thebreakdown thereof.

During such operation, substantially the entire voltage of rectifier I2is impressed across reactor [9, the impression of such voltage causinggap 5| to break down, whereby the magnetic energy stored in reactor i9is dissipated by the flow of induced current from reactor i9 throughresistor 54, gap 5| and the coil of relay l'l. Relay l1 accordinglyoperates to reverse the connections of 1,- battery l8 to thereby causeinterruption of the flow of current through rectifier I2. Suchinterruption is obtained without difiiculty because the magnetic energystored in reactor I9 is dissipated and therefore does not tend tomaintain the flow of current through rectifier l2. Such fiow of currenttherefore ceases upon the following passage through zero of the voltageimpressed on the anode carrying current at the time of operation ofrelay Upon complete dissipation of the magnetic energy of reactor I9,relay returns to the position shown to reestablish the flow of currentthrough rectifier l2. In the meanwhile, capacitors 22, 23 and 24 havingcompletely discharged through gap 4|, the gap and valve 5 have returnedto their normal operating condition and the entire system is thusreturned to normal operation within a period of time which need notexceed a small fraction of one second.

If the impedance of valve I accidentally collapses, the voltageresulting from the discharge of capacitor 23 impressed on gap 4! causessuch gap to break down. Gap 4|, which is partly coextensive with gap 41is accordingly rendered conductive, and capacitor 23 can dischargethrough the associated gap 4| instead of through valve 1. The system isthereafter returned to the normal operating condition in the mannerabove described with respect to valve 6. ihe present embodiment presentsthe advantage that there is no reactance in circuit with gap 4%, and thefiow of current through gap 4i may therefore be established veryrapidly. In the present instance, reactors I9, 26 and 2| substantiallyprevent the fiow of current from rectifier l2 and the discharge ofcapacitors 22 and 24 through valve 1.

If the impedance of valve 8 breaks down, the voltage appearing inwinding 53 as a result of the incipient discharge of capacitor 24through valve 8 is of sufficient magnitude to cause the space betweenelectrode 49 and one of the electrodes 4| to break down, so that gap 4|becomes conductive and discharges capacitor 24, thereby diverting theflow of current from valve 3. Ca-

pacitor 43 is connected in series with winding 43 to prevent theapplication, between electrode 49 and one of the electrodes 4|, of thefull voltage of rectifier 52 which would be sufficient to cause thebreakdown of the space between such electrodes.

Although but a few embodiments of the present invention have beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent:

1. In a protective system, an electric circuit, a source of electriccurrent connected with said circuit to cause fiow of currenttherethrough, an inductive winding in the connection between said sourceand said circuit, an incompletely conductive circuit connected inparallel with said circuit, and means responsive only to chan es in themagnitude of the flow of current through the first said circuit whenoccurring at a rate greater than a predetermined rate to cause conpletion of said incompletely conductive circuit.

2. In a protective system, an electric circuit comprising an element ofvariable conductivity to be protected against the fiow of excessivecurrent therethrough, a source of current connected with said circuitfor supplying current thereto,

cans for limiting the rate of change of fiow of current in said circuitcomprising a reactor included in the connections of said sourcetherewith, means for diverting the flow of current from said circuitupon the occurrence of a disturbance therein comprising a pair ofelectrodes defining a spark gap connection in parallel with saidcircuit, and means operable responsive to the magnitude of the rate ofincrease of flow of current in said circuit to cause breakdown of saidspark gap.

3. The combination with electric valve comprising a cathode and an anodehaving connections with a source of electric current and constitutingspaced electrodes for the flow of current therebetween, and means forlimiting the rate of change of said flow of current comprising a reactorincluded in th connections of said source of current with saidelectrodes, of means for diverting said flow of current from said valveupon the occurrence of a disturbance therein comprising a pair ofelectrodes defining a spark gap, and a transformer having a primarywinding connected in series with said anode and catl ode and a secondarywinding connected in series with said gap in a circuit connected inparallel with said primary winding and the said anode and cathode,whereby said gap breaks down upon the occurrence of an increase of saidflow of current at a rate greater than a predetermined rate.

4. In a protective system, an electric valve adapted to be connected toa source of electric current, through a reactor to limit the rate ofchange of the flow of current therebetween, a pair of electrodesdefining a spark gap, a transformer having a primary Winding connectedin series with said gap in a circuit connected in parallel with saidprimary winding and said valve whereby said gap breaks down uponincrease of the flow of current through said valve above a predeterminedrate, and a resistor connected in series with said valve to cause theflow of current through said valve to be diverted to said gap uponbreakdown of said valve.

5. The combination with a source of direct current, a capacitorconnected with said source of current to be charged therefrom, anelectric valve comprising a cathode and an anode connected in circuitacross said capacitor and receiving current from said source, meanscomprising a reactor included in the connections between said soLu'ceand said capacitor and said circuit for limiting the rate of changes offlow of current thereto, of means for diverting said flow of currentfrom said valve comprising a pair of electrodes defining a spark gapconnected in another circuit across said capacitor, a transformer havingwindings severally included in said circuits to impress potential acrosssaid spark gap of such magnitude as to cause breakdown of said gap uponthe occurrence of a flow of current increasing at a rate above apredetermined value through said valve, and a resistor in seriesconnection with said gap to damp the discharge of said capacitor throughsaid gap upon breakdown thereof.

6. The combination with an electric valve comprising a cathode and ananode having connections with a source of electric current andconstituting spaced electrodes for the fiow of current therebetween, andmeans comprising a reactor serially included in the connections betweensaid source and said electrodes for limiting the rate of change of saidflow of current, of means for diverting said flow of current from saidvalve upon the occurrence of a disturbance therein comprising atransformer having a primary winding connected in series with saidelectrodes and having a secondary winding, a pair of electrodesconnected with said secondary winding and defining a spark gap adjustedto break down upon increase of said fiow of current at a rate above apredetermined value, and a second pair of electrodes connected acrosssaid cathode and anode and said primary winding and defining a spark gappartly coextensive with the first said gap to become conductive uponbreakdown of the first said gap.

7. The combination with a source of direct current, a variableconductive electric valve comprising a cathode and an anode havingconnections with a source of electric current and constituting spacedelectrodes for the flow of current therebetween, and means comprising areactor serially included in the connections of said source of currentwith said electrodes for limiting the rate of change of said flow ofcurrent, of

means for diverting said flow of current from said electrodes upon adisturbance in said valve comprising a transformer having a primarywinding connected in series with said electrodes and having a secondarywinding, a capacitor having connections with one terminal of said sourceand with said secondary winding, a pair of electrodes defining a gapconnected across said secondary winding and said capacitor and adjustedto break down upon increase of said flow of current at a rate above apredetermined value, and another electrode connected with the otherterminal of said source and defining with the said electrode connectedwith the said one terminal of said source another spark gap partlycoextensive with the first said gap and becoming conductive uponbreakdown of the first said gap.

8. In combination, an electric valve of variable conductivity comprisinga cathode and an anode constituting spaced electrodes for the flow ofcurrent therebetween, a source of direct current connected with saidelectrodes to supply current thereto, a reactor included in theconnections of said source for maintaining the current suppliedtherefrom at a substantially constant value, a

capacitor connected in parallel with said electrodes and cooperatingwith said reactor for maintaining the flow of current supplied by saidsource at a substantially constant value and for supplying a variablecomponent thereof to said electrodes in response to variations of theconductivity of said valve, and means for diverting the said flow ofcurrent from said valve upon the occurrence of abnormal conditionstherein comprising an incompletely conductive circuit bridging saidelectrodes, and means operable retending to maintain the flow of currentof unidirection therebetween at a substantially constant value, acapacitor connected with the first said valve through said reactor tocooperate therewith in maintaining substantially uniform the flow ofcurrent between said valves and to supply a variable component thereofto said cathode and anode of the said second valve in dependence onvariations of the impedance thereof, means operable in response to asudden lowering of the impedance of the said second valve below apredetermined value for bridging the said cathode and anode by a circuitof such value as to divert said flow of current of unidirection from thesaid second valve, and means operating coordinately With the first saidmeans for rendering the first said valve non-conductive, whereby thefiow of current through said circuit is interrupted.

10. In combination, a source of alternating current, an electric valveof controllable conductivity connected with said source for convertingcurrent supplied therefrom into current of unidirection, a secondelectric valve of variable impedance comprising a cathode and an anodeconnected with the first said valve and receiving current ofunidirection therefrom, a reactor included in the connections betweensaid valves and tending to maintain the flow of current of unidirectionat a substantially constant value, a capacitor connected with the firstsaid valve through said reactor to cooperate therewith in maintainingsubstantially uniform the said current of unidirection and to supply avariable component thereof to the said cathode and anode of the saidsecond valve in dependence on variations of the impedance thereof, meansfor diverting said flow of current or" unidirection from the said secondvalve upon a sudden lowering of the impedance thereof below apredetermined value comprising a pair of electrodes forming a spark gap,a transformer having a primary winding connected in series with the saidcathode and anode and a secondary winding connected in series with saidgap in a circuit parallel with said primary winding and the said cathodeand anode, and means operable upon said sudden lowering of the impedanceof the second said valve to render the first said valve non-conductive,the last said means comprising a relay and electrodes defining anotherspark gap serially connected across said reactor.

11. In combination, a source of direct current, a plurality of reactorsconnected with one terminal of said source, a plurality of electricvalves of variable impedances each comprising a cathode and an anodeconnected between the other terminal of said source and the terminalfarthest from said source of a different one of said reactors andconstituting spaced electrodes for the flow of current supplied fromsaid source therebetween, a plurality of capacitors severally connectedin parallel with said valves, means for diverting current from one ofsaid valves comprising a pair of electrodes defining a spark gapconnected in parallel with the said cathode and anode thereof, atransformer having a primary winding in series connection with thecathode and anode of the said one of said valves and a secondary windingin series connection with said gap, whereby said gap becomes conductiveupon a sudden decrease of the impedance of the said one of said valvesto divert the resulting discharge current of the associated one of saidcapacitors therefrom, the said reactors delaying the discharge of theothers of said capacitors and the increase of current from said sourcethrough the said cathode and anode of the said one of said valves andthe said gap, and means operable responsive to the occurrence ofbreakdown of the impedance of the said one of said valves to causeinterruption of the said flow of current supplied from the said source.

FRANZ MERTENS.

